Other commands frequently used are START and ORBITAL (or SAVE) to modify the default records for starting and optimized orbitals, respectively. In open-shell cases, we recommend to use the WF, OCC, CLOSED, or OPEN cards to define the wavefunction uniquely.

The default behaviour can be modified either by options on the command line, or by directives. In such cases, the OCC and/or CLOSED directives can be used to force convergence to the desired state. Normally, this works well in closed-shell and many open-shell cases, but sometimes wrong occupations are obtained.

The Aufbau principle is used to determine the occupation numbers in each symmetry. By default, the number of electrons is equal to the nuclear charge, the spin multiplicity is 1 (singlet) for an even number of electrons and 2 (doublet) otherwise, and the wavefunction is assumed to be totally symmetric (symmetry 1) for singlet calculations. In contrast to older versions of molpro, the HF and RHF directives have identical functionality and can both be used for closed-shell or open-shell calculations. UHF or UHF-SCF, options calls the spin-unrestricted Hartree-Fock program

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